Bothering With Brackets Years 4 - 8

Summary Anyone can press buttons on a calculator and get answers. But deciding which buttons to press for more complex calculations is a problem to be solved. The idea in this activity is to encourage students to discuss how to use their calculator, no matter what type it is, to evaluate given 'sums' and to challenge them to find a way to check their calculator result. The focus is on how the tool is used and how we know that it has been used correctly. Materials One calculator per pair Samples of alternative calculators Some students may want to use their Poly Plug to justify their answers. Special Note Across our schools there are several types of simple four function calculator. The MathMaster and the MathMate both have order of operations (algebraic operating system) built in. The MathMate, regrettably discontinued by Texas, even has brackets on the keyboard as shown here. Other schools are using four function machines that don't have order of operations programmed. However, they all have memory function buttons, and even with an algebraic operating system there are some calculations that require these buttons.

Procedure Nothing generates discussion more certainly than pressing the same buttons on two types of calculator and getting different answers. If you don't have a MathMate/Master calculator available, at least get a scientific one from somewhere. These do have order of operations built in. However, understanding order of operations doesn't void the need for brackets, which are, of course, part of that order. For example:

Content division fraction calculations mathematical conversation operations - whole number order of operations problem solving recording - written using brackets

It is likely that most of us would confidently enter

However, if we are learning to predict answers before evaluating them with the calculator, we should be thinking twice about our confidence. Although the calculator has done exactly what you instructed, the correct answer is 5. Why? What else should have been keyed into the calculator and why? The answer will depend on the machine you are using.

How would you correctly enter:

The procedure in this activity is to use examples like these and a range of calculators to encourage group and class conversation about how and when to use the available buttons, especially the memory buttons. A key question will be:

As students become confident with these decisions ask them to:

• Prepare posters with examples showing when and how to use the buttons.
• Set complex calculations for each other to be evaluated on the calculator and checked some other way.

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